Fork lift with laterally travelling system

ABSTRACT

A fork lift with a laterally travelling system, wherein when a running mode is switched from a normal running in which right and left front wheels and rear wheels face in a longitudinal direction to a lateral running, rotating means is operated to rotate a turning member about a vertical axis in order to change the direction of the front wheels relative to that of a vehicle body, a change in running direction can be performed smoothly because the front wheels are formed integrally with a running drive device, and the front wheels are driven in forward and reverse directions by the running drive device after the front wheels are turned to face sideways so that a fork lift can run laterally and the rear wheels can be changed in direction in a follow-up manner by a turning caster system or can be changed in direction forcibly in the same manner as the front wheels, whereby the wheels of a drive system, though the fork lift is of a type capable of performing a normal forking operation, can be steered to face sideways so that it can run laterally to, for example, perform transportation of long materials with ease through a fork.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a division of application Ser. No. 09/980,555filed Oct. 23, 2001, which is a 371 of PCT/JP00/02693 which claimspriority from Japanese patent application nos. 11-117372 filed Apr. 26,1999, 11-117373 filed Apr. 26, 1999, 11-117375 filed Apr. 26, 1999,11-193811 filed Jul. 8, 1999, and 2000-32538 filed Feb. 10, 2000.

TECHNICAL FIELD

[0002] The present invention relates to a fork lift with a laterallytraveling system which can switch the fork lift to lateral running.

BACKGROUND ART

[0003] Conventionally, vehicles having a laterally travelling systemhave been seen among large-scale transporters, some kinds of loaders andthe like, and reach-type electric vehicle type fork lift devices.Furthermore, there are also side fork lifts for handling long materials,which have a mast or forks installed in a lateral direction with respectto the movement of the vehicle. However, there is no counter-type forklift which has a function similar to that of a side fork capable oflateral moving in addition to ordinary operational functions. In orderto achieve a fork lift of such kind, it is necessary to steer frontwheels which are drive wheels in a perfectly lateral direction.

[0004] More specifically, in a conventional fork lift 1 as illustratedin FIG. 23, a pair of right and left-hand front wheels (drive wheels) 3are provided to a front portion of a vehicle 2, a pair of right andleft-hand rear wheels (steering wheels) 4 are provided to a rear portionthereof, and a driver's room 5 is provided above the front portion ofthe vehicle 2. A vertically extendable mast 6 is provided in the frontend section of the vehicle 2 to be rotatable in the front-and-reardirection by means of a coupling axle 7 extending in the lateraldirection of the vehicle, and a tilt cylinder 8 for performingfront-and-rear rotation is provided between the vehicle 2 and the mast6.

[0005] The mast 6 comprises a pair of right and left-hand outer frames 9on the fork lift 1, and a pair of right and left-hand inner frames 10guided on the outer frames 9 to be able to move vertically, a liftcylinder 11 provided between the outer frames 9 and inner frames 10.Furthermore, a lift bracket 12 guided by the inner frames 10 to be ableto move vertically is provided, and a pair of right and left-hand forks13 are provided to this lift bracket 12 via a pair of upper and lowerfinger bars.

[0006] A seat 15, and a handle 16 or the like disposed to the front ofthis seat 15 are provided in the driver's room 5, and above theseelements, a head guard 19 is provided via front pipes 17 and rear pipes18 projecting from the vehicle body 2. A counter weight 20 is providedon the vehicle body 2, to the rear of the seat 15.

[0007] However, in the conventional fork lift 1 described above, sincethe right and left-hand front wheels 3 are driven by a common traveldrive, it is not possible to steer these front wheels 3 in a perfectlylateral direction, and hence lateral running cannot be achieved.

DISCLOSURE OF THE INVENTION

[0008] Therefore, it is a first object of the present invention toprovide a fork lift with a laterally travelling system so that the frontwheels forming the drive wheels can be steered to face directlysideways, whilst being capable of performing ordinary fork operations.

[0009] It is a second object of the present invention to provide a forklift with a laterally travelling system which allows adjustment oflinear movement and change of the direction of the vehicle body duringlateral running.

[0010] It is a third object of the present invention to provide a forklift with a laterally travelling system which permits the vehicle toreadily turn during lateral running.

[0011] It is a fourth object of the present invention to provide a forklift with a laterally travelling system which allows the front wheels tosteer, with the mast being disposed between the right and left-handfront wheels.

[0012] In order to achieve the first object described above, the forklift with a laterally travelling system according to the presentinvention is characterized in that a pair of right and left-hand frontwheels and a pair of right and left-hand rear wheels are provided in asteerable fashion on a vehicle body, the pair of right and left-handfront wheels are coupled respectively to driving shafts of travel drivedevices, both travel drive devices are installed on turning membersprovided rotatably about a vertical axis with respect to the vehiclebody, rotating means for performing rotation of the turning members isprovided, a mast is provided on the front end of the vehicle body, andforks are provided on the mast.

[0013] According to the present invention described above, during normalrunning, the right and left-hand front and rear wheels face in thefront-and-rear direction. Thereupon, by operating a lift lever, theforks are raised or lowered along the mast, and prescribed forkoperations can be performed. When switching from normal running tolateral running, rotating means is actuated first and the turningmembers are rotated about the vertical axis, whereby the front wheelscan be steered (to be in a perfectly lateral direction) with respect tothe vehicle body. Here, since the front wheels are respectively formedintegrally with running drive devices, it is possible to perform thisturning operation readily and smoothly. After steering the front wheelsin a perfectly lateral direction in this manner, the fork lift can becaused to run laterally in the right and left direction, by driving thefront wheels in the forward and reverse directions by means of thetravel drive devices. In so doing, follow-up steering of the rear wheelsis effected by means of a turning caster system, or alternatively, therear wheels are steered forcibly in a similar manner to the frontwheels.

[0014] In this way, in the present invention, it is possible to performlateral running by steering the driving front wheels so as to face in aperfectly lateral direction, while using normal fork operations. Henceit is possible to readily convey long materials, for example, by meansof the forks.

[0015] In order to achieve the second object described above, in thefirst aspect of the fork lift with a laterally travelling systemaccording to the present invention, the rotating means is constitutedsuch that the two turning members are operated to turn in mutuallyopposing directions by means of a common actuation device.

[0016] According to this first aspect of the invention, when switchingfrom normal running to lateral running, it is possible to steer thefront wheels (to a perfectly lateral direction) with respect to thevehicle body by actuating the common actuation device of the rotatingmeans so as to rotate the turning members in mutually opposing directionabout the vertical axes. In this manner, after steering the front wheelsto a perfectly lateral direction, the fork lift can be made to runlaterally in the right and left direction, by controlling and rotatingthe front wheels in mutually opposing directions by means of the traveldrive devices.

[0017] Moreover, when performing lateral running, in other words, inlateral running mode wherein the two front wheels are steered laterallywith respect to the vehicle body, it is possible to readily correctdeviation caused in the linear movement of the vehicle by road surfaceconditions or the weight balance of the vehicle, by slight actuation ofthe actuation device to steer the two front wheels inwards or outwardsby a small angle. Moreover, by steering the front wheels inwards oroutwards, the direction of the fork lift can also be changed to someextent during lateral running, and hence steering during lateral runningcan be performed.

[0018] Moreover, in a second aspect a fork lift with a laterallytravelling system according to the present invention, the rotating meanscomprises coupling sections of the turning members disposed in mutuallyopposing directions in the front-and-rear direction with respect to thevertical axis; a link member in the lateral direction of the vehicle,the link member being coupled between these coupling sections to enablethe turning members to be relatively rotatable; and an actuation devicefor moving this link member in the lateral direction of the vehicle.

[0019] According to this second aspect of the invention, it is possibleto steer the front wheels readily and reliably with respect to thevehicle body by moving the link member in the lateral direction of thevehicle, by means of the actuation device.

[0020] In order to achieve the third object described above, in thethird aspect of the fork lift with a laterally travelling systemaccording to the present invention, when the rotating means is operatedto rotate the turning members, the two drive wheels laterally directedare displaced in the front-and-rear direction.

[0021] According to this third aspect of the invention, by controllingand rotating the drive wheels by means of the travel drive devices,after the drive wheels have been steered to be in perfectly lateraldirections, in other words, by controlling and rotating the right andleft-hand drive wheels in such a manner that the rotational directionsand the speeds of revolutions thereof are the same, the fork lift can bemade to travel laterally in a right and left direction. Moreover, sincethe two drive wheels steered directed to be perfectly lateral aredisplaced in the front-and-rear direction of the vehicle, whenperforming lateral running, a turning force to the right or left can acton the vehicle, by simply differentiating the speeds of revolutions ofthe right and left-hand drive wheels by operating a handle or the like.Hence, lateral running can be performed while steering the vehiclereadily in the longitudinal direction (front-and-rear direction)thereof, and any deviation caused in linear movement of the vehicle bythe road surface conditions or the weight balance can be readilycorrected.

[0022] In order to achieve the fourth object described above, in afourth aspect of a fork lift with a laterally travelling systemaccording to the present invention, the mast is installed between theright and left-hand front wheels at the front end of the vehicle to berotatable in the front-and-rear direction by means of a coupling axledisposed in the lateral direction of the vehicle above the front wheels,a rotational drive device for effecting front-and-rear rotation isprovided between the vehicle body and the mast, and when the mast isrotated by this rotational drive device, the lower section of the mastis moved to a position where the mast does not interfere with thesteering of the front wheels.

[0023] According to this fourth aspect of the present invention, duringnormal running, the mast assumes an upright attitude, the lower sectionthereof being disposed between the right and left-hand front wheels, andhence the fork lift can be formed without creating a long frontoverhang. The operation of switching from normal running to lateralrunning can be performed by rotating (inclining) the mast about thecoupling axle by operating the rotating drive device and moving thelower section thereof to a position where the mast does not interferewith the steering of the front wheels, steering the front wheels to a90° position (to be directed laterally) with respect to the vehiclebody, and rotating the mast about the coupling axle by reverse operationof the rotating drive device to return the mast to the upright attitude.Thereby, the fork lift can be made to travel laterally, while performingsmooth turning without any hindrance and without creating a long frontoverhang.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a side view of a fork lift with a laterally travellingsystem during normal running, illustrating a first embodiment of thepresent invention;

[0025]FIG. 2 is a partially cutaway front view of a front wheel sectionof the fork lift with a laterally travelling system;

[0026]FIG. 3 is a schematic plan view of the fork lift with a laterallytravelling system during normal running;

[0027]FIG. 4 is a schematic plan view of the fork lift with a laterallytravelling system during lateral running;

[0028]FIG. 5 is a side view of a fork lift with a laterally travellingsystem during normal running, illustrating a second embodiment of thepresent invention;

[0029]FIG. 6 is a partially cutaway front view of a front wheel sectionof the fork lift with a laterally travelling system;

[0030]FIG. 7 is a schematic plan view of the fork lift with a laterallytravelling system during normal running;

[0031]FIG. 8 is a schematic plan view of the fork lift with a laterallytravelling system during lateral running;

[0032]FIG. 9 is a side view of a fork lift with a laterally travellingsystem during normal running, illustrating a third embodiment of thepresent invention;

[0033]FIG. 10 is a partially cutaway front view of a front wheel sectionof the fork lift with a laterally travelling system;

[0034]FIG. 11 is a plan view of a lateral running operating section ofthe fork lift with a laterally travelling system;

[0035]FIG. 12 is a schematic plan view of the fork lift with a laterallytravelling system during normal running;

[0036]FIG. 13 is a schematic plan view of the fork lift with a laterallytravelling system during lateral running;

[0037]FIG. 14 is a schematic plan view of the fork lift with a laterallytravelling system during lateral running adjustment;

[0038]FIG. 15 is a side view of a fork lift with a laterally travellingsystem during normal running, illustrating a fourth embodiment of thepresent invention;

[0039]FIG. 16 is a partially cutaway front view of a front wheel sectionof the fork lift with a laterally travelling system;

[0040]FIG. 17 is a plan view of a front wheel section of the fork lift,(a) during linear running and (b) during lateral running;

[0041]FIG. 18 is a schematic plan view of the fork lift with a laterallytravelling system, (a) during linear running and (b) during lateralrunning;

[0042]FIG. 19 is a schematic plan view of the fork lift with a laterallytravelling system, (a) during steering of the rear section and (b)during steering of the front section;

[0043]FIG. 20 is a schematic plan view of the fork lift with a laterallytravelling system, (a) during linear running and (b) during lateralrunning;

[0044]FIG. 21 is a side view of a fork lift with a laterally travellingsystem during normal running, illustrating a fifth embodiment of thepresent invention;

[0045]FIG. 22 is a side view of the fork lift with a laterallytravelling system during lateral running; and

[0046]FIG. 23 is a side view of a fork lift, illustrating an example ofa prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0047] A first embodiment of the present invention is described belowwith reference to FIG. 1 to FIG. 4.

[0048] In the first embodiment, constituent elements which are the sameor substantially the same as those in the prior art example (FIG. 23)described above are similarly labelled, and further explanation thereofis omitted here. Specifically, 1 is a fork lift, 2 is a vehicle body, 3are front wheels (drive wheels), 4 are rear wheels (steering wheels), 5is a driver's room, 6 is a mast, 7 is a coupling axle, 8 is a tiltcylinder, 9 is an outer frame, 10 is an inner frame, 11 is a liftcylinder, 12 is a lift bracket, 13 is a fork, 15 is a seat, 16 is ahandle, 17 is a front pipe, 18 is a rear pipe, 19 is a head guard, and20 is a counterweight.

[0049] The pair of right and left-hand front wheels 3 and the pair ofright and left-hand rear wheels 4 are provided such that they arerespectively steerable to be angled 90° (steerable in a perfectlylateral direction) with respect to the vehicle body 2. Morespecifically, the pair of right and left-hand front wheels 3 are coupledto hydraulic motors 21 by means of rims 3A thereof being respectivelyattached directly to a rotating flange (one example of a driving shaft)22 of the hydraulic motor (one example of a travel drive) 21, via acoupling tool 23.

[0050] A mount of each hydraulic motor 21 is attached in a lateraldirection to a vertical plate section of an inverse L-shaped turningmember 24. A lateral plate section of the turning member 24 is providedto the vehicle body 2 to be rotatable about a vertical axis 27 via abearing 25 and a vertical axle 26. In this case, the vertical axis 27 ispositioned directly above the front wheel 3. The right and left-handturning members 24 are coupled by means of a link 28 or the like, andare rotated by means of a common turning cylinder (an example ofrotating means) 29, whereby the right and left-hand front wheels 3 arecaused to steer in mutually opposing directions in such a manner thatthey face in a perfectly lateral direction.

[0051] An engine 30 and a pair of hydraulic pumps 31 driven by theengine 30 are provided on the vehicle body 2. The correspondinghydraulic pumps 31 and the hydraulic motors 21 are coupled by means oftubes (hydraulic hoses or the like) 32 in such a manner that thehydraulic pumps 31 correspond respectively to one of the hydraulicmotors 21, in other words, in such a manner that a two-pump two-motortype hydraulic drive system (HST system) is formed.

[0052] Rims 4A of The pair of right and left-hand rear wheels 4 areinstalled in such a manner that respective rims 4A thereof are rotatablewith respect to the vertical plate section of a turning member 34. Thelateral plate section of each turning member 34 is provided to thevehicle body 2 to be rotatable about a vertical axis 37 by means of abearing 35 and a vertical axle 36. In this case, the vertical axis 37 ispositioned directly above the rear wheel 4. In other words, the pair ofright and left-hand rear wheels 4 are steered in a follow-up steeringmanner by use of a turning caster system.

[0053] Explained below is the operation in the first embodimentdescribed above.

[0054] The solid lines in FIG. 1 and FIG. 2, and FIG. 3 illustrate astate of normal running, where the right and left-hand front wheels 3and the right and left-hand rear wheels 4 are facing in thefront-and-rear direction. A fork lift 1 of this kind can be driven totravel by an operator seated on the seat 15 in the driver's room 5 andoperating the handle 16.

[0055] By operating a lift lever to actuate the lift cylinder 11, thefork 13 can be raised or lowered along the mast 6 via the lift brackets12 and the like, and hence required fork operations can be performed.Further, by operating the tilt lever to actuate the tilt cylinder 8, themast 6 can be rotated (inclined) about the coupling axle 7, andtherefore the attitude of the forks 13 can be changed via the liftbrackets 12 or the like.

[0056] When changing from such a normal running mode to a lateralrunning mode, a lever-type lateral mode switch (not shown) is operatedfirst, then the turning cylinders 29 are actuated by inclining thelever, and the turning members 24 are rotated about the vertical axis 27via the link 28. Thereby, as illustrated by the virtual lines in FIG. 1and FIG. 2 and in FIG. 4, the front wheels 3 are steered 900 (steered tobe in a perfectly lateral direction) with respect to the vehicle body 2.

[0057] Here, since the front wheels 3 are respectively formed integrallywith the hydraulic motors 21, this steering to a 90° position isperformed smoothly. Further, since each vertical axes 27 are positioneddirectly above the front wheels 3, the front wheels 3 or the like can besteered to a 90° position in a compact manner.

[0058] Steering of the front wheels 3 in this manner, in other words,the steering of the front wheels 3 to be in a perfectly lateraldirection is detected by a sensor which makes an indicator lamp to lightup, whereby the lateral running mode can be assumed consequently, bysupplying hydraulic pressure from the pair of hydraulic pumps 31 drivenby the engine 30 to the corresponding hydraulic motors 21 via the pipes32, according to the forward or reverse control performed in thedriver's room 5, the front wheels 3 are driven in the forward or reversedirection, and hence the fork lift 1 can travel laterally in the left orright direction. In so doing, the pair of rear wheels 4 forming aturning caster system perform follow-up steering.

[0059] By performing lateral running in this way, it is possible, forexample, to readily convey elongate objects by means of the forks 13.Correction of linearity in the lateral running can be readily performedby minute operation of the turning cylinders 29 by inclining the leverin the front-and-rear direction so as to perform minute adjustment ofthe angle of the front wheels 3.

[0060] Moreover, by adopting a two-pump two-motor type hydraulic drivesystem for the drive of the fork lift 1, the steering during normalrunning as described above can be performed by controlling the directionof rotations of the front wheels 3 and the difference in number ofrotations thereof by means of a handle wheel, but in the lateral runningmode, this steering system is stopped electrically.

[0061] Next, a second embodiment of the present invention is describedwith reference to FIG. 5 to FIG. 8.

[0062] In this second embodiment, constituent elements which are thesame or substantially the same as those in the first embodimentdescribed above (FIG. 1-FIG. 4) are similarly labelled, and detailedexplanation thereof is omitted here.

[0063] The pair of right and left-hand front wheels 3 are coupled toelectric motors 41 by means of the rims 3A thereof respectively attacheddirectly to a rotating flange (driving shaft) 42 of the electric motor(another example of a travel drive) 41 by means of a coupling tool 23. Abattery 43 is mounted in the vehicle body 2, and a controller 44 isattached to this battery 43. A cable 45 from the controller 44 isconnected respectively to each electric motor 41.

[0064] Explained below is the operation in the second embodimentdescribed above.

[0065] The solid lines in FIG. 5 and FIG. 6 and the diagram in FIG. 7illustrate a normal running mode, where the right and left-hand frontwheels 3 and the right and left-hand rear wheels 4 are facing in thefront-and-rear direction. Therefore, by supplying electric power of thebattery 43, which has been controlled by the controller 44, to therespective electric motors 41 via the cables 45, the front wheels 3 aredriven in forward and reverse directions, whereby the fork lift 1 cantravel forwards or rearwards.

[0066] When switching from this normal running mode to a lateral runningmode, as illustrated by the virtual lines in FIG. 5 and FIG. 6 and inthe diagram in FIG. 8, the front wheels 3 are steered to a 90° positionwith respect to the vehicle body 2 (steered to be in a perfectly lateraldirection). Since the front wheels 3 are integrally formed with theelectric motors 41, respectively, this steering to a 90° position isperformed readily and smoothly.

[0067] Steering of the front wheels 3 in this manner is detected by asensor which makes an indicator lamp to light up, whereby the lateralrunning mode is entered. Therefore, by supplying the electric power ofthe battery 43, which has been controlled by the controller 44, to therespective electric motors 41 via the cables 45, the front wheels 3 aredriven forwards or rearwards, whereby the fork lift 1 can travellaterally in the left or right direction.

[0068] Next, a third embodiment of the present invention will bedescribed with reference to FIG. 9 to FIG. 14.

[0069] In the third embodiment, constituent elements which are the sameor substantially the same as those in the first embodiment describedabove (FIG. 1 to FIG. 4) are similarly labelled, and further explanationthereof is omitted here.

[0070] Rotating means 50 for causing rotation of the turning members 24is provided, and this rotating means 50 is constituted in such a mannerthat the turning members 24 are caused to turn in mutually opposingdirections by a common actuation device. In other words, vertical pins(one example of a coupling section provided on the turning member) 51are provided respectively on the lateral plate sections of both rotatingmembers 24 in such a manner that the two vertical pins 51 are positionedin opposite directions with respect to the vertical axis 27,respectively, to the front and to the rear of the vertical axis 27.

[0071] A link member 52 is provided in the lateral direction of thevehicle, and either end of this link member 52 is coupled in arelatively rotatable fashion to one of the aforementioned vertical pins51. A turning cylinder (one example of an actuation device) 53 forcausing the link member 52 to move in the lateral direction of thevehicle, is provided between the vehicle body 2 and the link member 52at the central portion in the longitudinal direction thereof. Oneexample of rotating means 50 is constituted with the elements 51-53 andthe like.

[0072] The rear wheel 54 is constituted by a parallel pair of right andleft-hand wheels, the respective rims 54A of which are attachedrotatably to vertical plate sections of a common turning member 55, andthe lateral plate section of this turning member 55 is providedrotatably about a vertical axis 58, with respect to the vehicle body 2,by means of a bearing 56 and vertical axle 57. In this, the verticalaxis 58 is positioned in the central portion between the two rear wheels54. This means that the rear wheels 54 are steered in a follow-upsteering manner by means of the caster system.

[0073] The operation in the third embodiment of the present inventiondescribed above will be explained below.

[0074] The solid lines in FIG. 9 and FIG. 10, and the diagrams in FIG.11(a) and FIG. 12 illustrate a normal running mode. By retracting theturning cylinder 53 and causing the link member 52 to move in thedirection of retraction, the right and left-hand front wheels 3 and therear wheels 54 are oriented in the front-and-rear direction.

[0075] When switching from normal running of this kind to lateralrunning, firstly, a lever-type lateral running mode switch (not shown)is operated, and by inclining a lever, the turning cylinder 53 is causedto extend. Thereby, the link member 52 is moved in the direction of theextension, and in accordance with this movement, the turning members 24are rotated about the vertical axis 27.

[0076] Since the link member 52 is positioned in a crossing manner withrespect to the right and left front wheels 3, as illustrated by thevirtual lines in FIGS. 9 and 10 and the diagrams in FIG. 11(b) and FIG.13, the two turning members 24 rotate in mutually opposite directionsabout the vertical axis 27, whereupon the two front wheels 3 are steeredto a 90° position (in a perfectly lateral direction) with respect to thevehicle body 2.

[0077] After steering the front wheels 3 in this fashion, by supplyinghydraulic pressure from the pair of pumps 31 driven by the engine 30 tothe corresponding hydraulic motors 21 by means of the pipes 32, thefront wheels 3 are driven forwards and rearwards, and hence the forklift 1 is enabled to travel laterally in the right and left direction.In so doing, the hydraulic motors 21 corresponding to the right andleft-hand front wheels 3 are controlled in such a manner that theyrotate in opposite directions. The right and left-hand pair of rearwheels 54 forming a turning caster system perform follow-up steering.

[0078] When performing lateral running in this manner, in other words,in a lateral running mode where the front wheels 3 are steered to a 90°position with respect to the vehicle body 2 (in a perfectly lateraldirection), the turning cylinder 53 is slightly retracted to steer thefront wheels 3 inwards by a small angle (in a range of about 5°) asillustrated in FIG. 14(a), or the turning cylinder 53 is slightlyextended to steer the front wheels 3 outwards by a small angle (in arange of about 5°) as illustrated in FIG. 14(b), whereby deviation froma straight course caused by road surface conditions or due to weightbalance can be readily corrected.

[0079] By steering (moving) the front wheels 3 inwards or outwards by asmall angle (in a range of about 5°), it also becomes possible to changethe direction of the fork lift 1 to some extent during lateral running.Further, if it is structurally permitted, by taking the steering angleof the front wheels 3 to be greater than 5°, it also becomes possible toperform turning during lateral running.

[0080] In the third embodiment described above, the rear wheel 54 wasdescribed as a parallel pair of right and left-hand wheels, but it isalso possible to adopt a pair of right and left-hand rear wheels 54disposed similarly to the front wheels 3. In this case, one of the pairof right and left-hand rear wheels 54 may be of a steering-typecontrolled by a handle wheel and the other may be of a turningcaster-type, and when switching to lateral running, the former one ofthe rear wheels 54 is forcibly steered by means of a cylinder or thelike.

[0081] Next, a fourth embodiment of the present invention will bedescribed with reference to FIG. 15 to FIG. 20.

[0082] In this fourth embodiment, constituent elements which are thesame or substantially the same as those in the first embodimentdescribed above (FIG. 1-FIG. 4) are similarly labelled, and detailedexplanation thereof is omitted here.

[0083] The mounts of hydraulic motors 21 are attached in a lateraldirection to vertical plate sections of T-shaped turning members 60, andthe lateral plate sections of the turning members 60 are installedrotatably about a vertical axis 63 with respect to the vehicle body 2via a bearing 61 and vertical axle 62. Here, a vertical axis 63 ispositioned away from a front wheel ground contact axis 64 located at thecentral portion of the front wheel 3, with a space equal to alateral-directional displacement L therebetween.

[0084] Rotating means 70 for rotating the turning members 60 isprovided, and this rotating means 70 is constituted in such a mannerthat the two turning members 60 are turned in the same direction bymeans of a common actuation device. In other words, the rotating means70 comprises a turning cylinder (one example of a common actuationdevice) 71, and a main body 71 a of this turning cylinder 71 isinstalled swingably on the vehicle body 2 via a vertical pin 72. Apiston rod 71 b is coupled in a relatively rotatable fashion to a link73 fixed to one of the turning members 60 via a vertical coupling pin74.

[0085] Two arms 75 projecting from the right and left-hand verticalaxles 62 are mutually coupled in a relatively rotatable fashion by meansof a link member 76 and coupling pins 77. The two coupling pins 77 aredisposed in the same front-and-rear direction with respect to thevertical axes 63, and consequently, when the right and left-hand frontwheels 3 are steered in the front-and-rear direction, the link member 76is positioned parallel to the front wheel axis between the two frontwheels 3.

[0086] Therefore, by actuating the turning cylinder 71 to rotate one ofthe turning members 60 via the link 73, one of the front wheels 3 on oneside is steered about the vertical axis 63 and caused to face directlysideways, and the other front wheel 3 is steered about the vertical axis63 and caused to face directly sideways by means of the arm 75, linkmember 76 and the like. In other words, with the rotating means 70, byactuating the common turning cylinder 71, the right and left-hand frontwheels 3 are rotated (steered) mutually in the same direction to faceperfectly sideways respectively. The elements 71 to 77 and the likeconstitute one example of the rotating means 70.

[0087] The operation of the fourth embodiment described above will beexplained below.

[0088] The solid lines in FIG. 15 and FIG. 16, and the diagrams in FIG.17, FIG. 18 and FIG. 20(a) illustrate linear movement during normalrunning, in which the pair of right and left-hand front wheels 3 and thepair of right and left-hand rear wheels 4 are facing in a front-and-reardirection. Here, the rotating means 70 operates such that the turningcylinder 71 is extended, the link 73 is moved in this direction ofextension, and the link member 76 is placed in parallel to the frontwheel axis, so that the right and left-hand front wheels 3 are orientedin the front-and-rear direction.

[0089] As described above, a two-pump two-motor type hydraulic drivesystem is adopted as a driving system for the fork lift 1, so thatturning during linear movement in a normal running mode can be effectedby controlling the steering direction of the two front wheels 3 and thedifference in revolutions thereof by means of the handle wheel. In otherwords, as illustrated by virtual lines in FIG. 18(a), for example, whenspeed of revolutions on the right-hand side, F, is raised higher thanthe speed of revolutions on the left-hand side, f, the fork lift 1 willperform a left-hand turn due to the resulting difference in revolutions.In this case, the right and left pair of rear wheels 4 will perform afollow-up turning while automatically changing the orientation thereofto the direction of the steering. A right-hand turn can be performed ina similar manner by increasing the speed of revolutions on the left-handside to be higher than that on the right-hand side.

[0090] When switching from normal running of this kind to lateralrunning, a lever-type lateral running mode switch (not shown), forexample, is operated first, and then the rotating means 70 is actuated.More specifically, in the rotating means 70, the turning cylinder 71 iscaused to retract by inclining the lever. Thereby, one of the turningmembers 60 is rotated about the vertical axis 63 via the link 73 and thelike, whilst the other turning member 60 is rotated about the verticalaxis 63 by means of the vertical axle 62, arm 75, link member 76 and thelike.

[0091] Since the link member 76 is positioned in parallel to the frontwheel axis, the two turning members 60, as illustrated by the virtuallines in FIG. 15 and FIG. 16, and the diagrams in FIG. 17, FIG. 18 andFIG. 20(b), are rotated in the same direction about their vertical axes63, and the two front wheels 3 are steered to a 90° position (in aperfectly lateral direction) with respect to the vehicle body 2.Moreover, since the vertical axes 63 are distanced from the respectivefront wheel ground contact axes 64 by a space equal to thelateral-directional displacement L, the two front wheels 3 which havebeen steered to a 90° position (in a perfectly lateral direction) to bedirected laterally are distanced from each other in the front-and-reardirection by a displacement in lateral movement, 2L, that is double thedisplacement L.

[0092] By steering the front wheels 3 to a 90° position in this way, thelateral running mode can be assumed. Consequently, by supplying thehydraulic pressure from the pair of hydraulic pumps 31 to thecorresponding hydraulic motors 21, the front wheels 3 are driven inforward and reverse directions, and the fork lift 1 can perform lateralrunning in the right-and-left direction, as illustrated in FIG. 18 andFIG. 20(b). Here, during lateral running in a linear direction, thehydraulic motors 21 corresponding to the right and left-hand frontwheels 3 are controlled in such a manner that the respective directionsof rotation and revolutions are the same.

[0093] When lateral running is performed in this way, in other words,when the lateral running mode in which the two rear wheels 4 are steered90° (in a perfectly lateral direction) with respect to the vehicle body2 is taken as a neutral state, and a steered angle of the handle 16 orrear wheels 4 from this state is detected by a sensor or the like, andby changing the input and output to and from the hydraulic controller,different speeds of revolutions are given to the right and left-handfront wheels 3 respectively, thereby to effect turning.

[0094] In other words, in lateral running to the right-hand side asillustrated in FIG. 19(a), if the right-hand side front wheel 3 is setto a high speed of revolutions F and the left-hand side front wheel 3 isset to a low speed of revolutions f, a right-hand turning force acts onthe vehicle body 2 due to the difference in speed of revolutions betweenthe front wheels 3 which are distanced by the lateral runningdisplacement of 2L, and lateral running to the right is performed whileturning towards the rear side. Moreover, in lateral running to theright-hand side as illustrated in FIG. 19(b), if the left-hand sidefront wheel 3 is set to a high speed of revolutions F and the right-handside front wheel 3 is set to a low speed of revolutions f, a left-handturning force acts on the vehicle body 2 due to the difference inrevolutions between the two front wheels 3 distanced by the lateralrunning displacement 2L, and lateral running to the right-hand side isperformed while steering towards the front side.

[0095] In lateral running of this kind, since a lateral runningdisplacement 2L arises between the two front wheels 3, a turning forceto the left or right can be applied to the vehicle body 2, simply byapplying different speeds of revolution to the right and left wheels ofthe front wheels 3 by way of operating the handle or the like, and hencelateral running can be performed whilst turning the vehicle in thelongitudinal direction (front-and-rear direction) thereof. Further, itis possible to readily correct deviation from the straight course causedby the road surface conditions or the weight balance. Similar controlcan be also achieved during lateral running to the left-hand side.

[0096] In the fourth embodiment described above, a system wasillustrated in which the turning cylinder 71 is used as an actuationdevice of the rotating means 70, this may also comprise a system wherethe steering to a 90° position is performed by means of a motor or thelike. Moreover, the rotating means 70 was described as such that theturning cylinder 71 is used as a common actuation device for the rightand left-hand wheels, but it is also possible to provide separateactuation devices on the right and left-hand sides.

[0097] Next, a fifth embodiment of the present invention is describedwith reference to FIG. 21 and FIG. 22.

[0098] In this fifth embodiment, constituent elements which are the sameor substantially the same as those in the first embodiment describedabove (FIG. 1-FIG. 4) are similarly labelled, and detailed explanationthereof is omitted here.

[0099] The pair of right and left-hand front wheels 3 and the pair ofright and left-hand rear wheels 4 are provided respectively to besteerable 90° (laterally steerable) with respect to the vehicle body 2.The front wheels 3 are drive wheels, and each comprises an actuationdevice for performing a 90° steering. The mast 6 disposed at the frontend of the vehicle body 2 is disposed such that the lower portionsthereof are positioned between the right and left-hand front wheels 3when in an upright attitude. The mast 6 is attached rotatably in thefront-and-rear direction with respect to the vehicle body 2 by means ofa coupling axle 80 which is positioned in the lateral direction of thevehicle and above the front wheels 3.

[0100] A tilt cylinder 81, which is an example of a rotational drivedevice for performing front-and-rear rotation of the mast 6, is providedbetween the mast 6 and the vehicle body 2. When the mast 6 is rotated bythe tilt cylinder 81, the lower portions of the mast 6 swings outforwards and moves to a position where the mast does not interfere withthe steering of the front wheels 3.

[0101] The operation of the fifth embodiment of the present inventiondescribed above will be explained below.

[0102] The solid lines in FIG. 21 show a normal running mode. Here, thetilt cylinder 81 is retracted so that the mast 6 is in a standingposition and the lower portion thereof is positioned between the rightand left-hand front wheels 3. Therefore, the fork lift 1 can be formedwithout creating a long front overhang. By operating the tilt lever andactuating the tile cylinder 81, the mast 6 can be rotated (tilted) aboutthe coupling axle 80, and hence the attitude of the forks 13 in the forklift 1 can be changed via the lift brackets 12 and the like.

[0103] When switching from normal running of this kind to lateralrunning, a lateral running mode switch (not shown) is operated first,and the tilt cylinder 81 is extended greatly. By extending the tiltcylinder 81, the mast 6 is rotated (tilted) about the coupling axle 80,and as illustrated by the dotted lines in FIG. 21, the lower section ofthe mast 6 swings out forwards from between the front wheels 3, andmoves to a position where the mast does not interfere with the steeringof the front wheels 3.

[0104] Next, the turning lever (not shown) is operated, and the frontwheels 3 are steered to a 90° position (steered perfectly laterally)with respect to the vehicle body 2, by a 90° -steering-operation device,as illustrated by the virtual lines in FIG. 1. In this, the 90° steeringof the front wheels 3 is performed smoothly without any hindrancebecause the lower section of the mast 6 has been moved to the positionwhere the mast does not interfere with the steering.

[0105] After performing the steering of this kind, the tilt cylinder 81is actuated to retract itself by the feedback from the sensor. Thereby,the mast 6 is rotated about the coupling axle 80 to assume a standingposition, as illustrated in FIG. 22, and the lower section of the mast 6is made to oppose the side faces of the front wheels 3 from the forwarddirection, so that the fork lift 1 can perform lateral running, withoutthe front overhand becoming long.

[0106] In the fifth embodiment described above, the tilt cylinder 81 wasdescribed as a rotation drive device, but this may be a screw drive, alinkage system or the like.

[0107] In the respective embodiments described above, the turning castersystem which performs follow-up steering was adopted as the pair ofright and left-hand rear wheels 4, or for the parallel pair of right andleft-hand rear wheels 54, but similarly to the front wheels 3, suchsystem as to effect turning forcibly by means of a cylinder or the likemay be adopted. Moreover, it is also possible to adopt a steering-typewheel operated by the handle wheel as one of the rear wheels 4, and aturning caster-type wheel as the other rear wheel 4. In this case, whenswitching to lateral running, the former rear wheel 4 is forciblysteered by a cylinder or the like.

1. A fork lift with a laterally traveling system including a pair ofright and left-hand front wheels and a pair of right and left-hand rearwheels each provided on a vehicle body, characterized in that: the frontwheels and the rear wheels are respectively provided to be steerable;the pair of right and left-hand front wheels are respectively coupled inlinkage to driving shafts of travel drive devices; each of said traveldrive devices is attached to turning members provided to be rotatableabout a vertical axis with respect to the vehicle body, and rotatingmeans is provided for rotating the turning members; and a mast isprovided on the front end of the vehicle body, and forks are provided onthe mast; said mast being installed between the right and left-handfront wheels at a front end of the vehicle to be rotatable in thefront-and-rear direction by means of a coupling axle positioned in thelateral direction of the vehicle above the front wheels, and arotational drive device for effecting front-and-rear rotation isprovided between the vehicle body and the mast, whereby when the mast isrotated by this rotational drive device, the lower section of the mastis moved to a position where the mast does not interfere with steeringof the front wheels.